The mod-ui and mod-host may be having an exclusive connection to each other, so they don’t respond to other communication. The pedals themselves are instance of LV2 plugins. I think you should be able to try to access them directly using some LV2 library, like liblibv, as suggested in this topic: TouchOSC + Modep - Toggles and presets. Make sure to set the LV2_PATH to be able to see the same lv2 plugins.
Also check out this script: https://github.com/BlokasLabs/modep-btn-scripts/blob/master/modep-ctrl.py, it does some web requests to get and set information through mod-ui.
See https://github.com/BlokasLabs/mod-ui/blob/modep-1.8/mod/webserver.py#L1934 for the registered URL endpoints.